(1) Field of the Invention
The present invention relates to a method for disbursing information into a memory matrix, and more particularly to a method for multiple stage matrix interleaving of a digital information bit stream.
(2) Description of the Prior Art
Because of their huge storage capacity and relatively low cost, laser optical discs are being adapted for many new high density digital information storage applications. By comparison, a laser optical disc has the storage capacity of 12,500,000 million characters, whereas a hard magnetic disc has the storage capacity of 2.5 million characters. Laser optical discs have been utilized for some time as the information storage medium in home video replay systems priced within the means of many consumers. Although the video signal recorded in such systems is analog, interactive video disc systems have been developed which record digital information on the laser optical disc along with video information, such as computer programs, textual computer files, audio, and the like.
However, one difficulty with laser optical discs is that frequent burst errors or dropouts are encountered therewith, which severely affect the integrity of any information recorded thereon. Although such dropouts are a problem in regard to the integrity of analog information, such as video in the previously mentioned replay systems, it presents a much greater problem in regard to digital information. Furthermore, this difficulty is compounded in the replication process presently utilized for the laser optical discs that are distributed with video and audio recorded thereon for playback by such replay systems. In this replication process, the information to be recorded is organized or formatted in a video tape recorder (vTR) from which it is passed for recording on the laser optical disc.
As is true for any magnetic recording medium, the tape of the VTR is also the cause of frequent dropouts which are actually a gap or void in the information and are usually caused by a defect on the magnetic medium. One example of such a defect is the stipples or bumps of magnetic oxide which occur periodically on a magnetic recording medium. The stipples cause the record and/or replay transducer head to bounce or jump off the magnetic medium and thereby result in information gaps during the time that the transducer head is displaced from the magnetic medium. In regard to digital information, such gaps obliterate two or more successive bits of information, which is the criteria that distinguishes burst error or dropout from single bit or random error.
Although various error correction codes have been utilized in regard to digital information to effectively cope with dropout, such codes tend to be complex and such complexity increases in proportion to the level of integrity desired for the information. Of course, the greater the complexity of the error correction code, the greater the number of check bits that must be disposed in each byte of information, and the greater the complexity and cost of the hardware associated with such error correction. Furthermore, both the operational response time of such hardware and the information storage capacity of the recording medium are decreased proportionally, as the number of check bits per byte of information is increased.
To enhance the effectiveness of less complex error correction codes, single stage interleaving has been utilized to reduce the effect of dropout, such as disclosed in U.S. Pat. No. 4,217,660 to En. With such interleaving, consecutive bytes of digital information are first written into a matrix, row by row or column by column. Then a bit stream is read out from the matrix, column by column or row by row, respectively, with the bits which were adjacently disposed previously in each byte of digital information separated therein by the distance of either one column or one row of bits. Due to such separation, when such bit stream is recorded, more than one bit in any byte of digital information is less likely to be affected by dropout and error correction is therefore simplified. Furthermore, the possibility that more than one bit in any byte of digital information will be affected by both dropout and random error is greatly reduced. Consequently, such interleaving permits error correction codes of relatively minor complexity to be used, such as the Hamming Code which, for any byte of digital information, will only correct a single bit error and detect double bit errors (error affecting two bits in a sequence).
In other single stage matrix interleaving, more sophisticated error correction codes are utilized and are added to the digital information after entry thereof into the matrix, such as disclosed in U.S. Pat. No. 4,495,623 to George et al.